AsyncAPI support

[musjj]

Description of the feature

https://www.asyncapi.com

AsyncAPI is a specification for defining asynchronous APIs. It's a superset(-ish) of OpenAPI, but it supports features like websockets, which was rejected by OpenAPI.

Like OpenAPI, AsyncAPI is also a part of the Linux Foundation, so it's a pretty well-established project with solid grounding.

It would be nice if we can create type-safe AsyncAPI services with poem, just like with OpenAPI.